The U.S.’s biggest “low fare” airline appears to be experiencing an identity crisis. In Southwest’s new ad campaign, there’s no silly humor and no mention of “bags fly free” or cheap flight prices. The message is that this is a different airline — one that longtime customers may feel is hard to recognize or even like.

“The campaign is a departure in tonality for Southwest, and we hope it inspires our customers,” Southwest executive Bob Jordan said in a press release announcing its new commercial, which debuted during the NCAA March Madness basketball tournament. “Southwest has changed a lot over the years, we keep getting better, and we want customers to see us in a new light.”

The ad will come as “a shock” to TV viewers, according to the Chicago Business Journal, because of the disappearance of “all the silly, cartoonish aspects of its advertising.” The ad features no goofball humor, nor any messages about Southwest’s low fares or its value-laden “bags fly free” policies that tell the masses “you are now free to move about the country.” Instead, the commercial is filled with images of people diligently going about their jobs, as well as heartwarming clichés like “The American dream just doesn’t happen. It’s something you have to work for.”

The image of Southwest as a plucky upstart taking on the industry giants is, in other words, totally gone. We’re left with the Southwest logo and a voice-over claiming its status as “America’s largest domestic airline.”

Among travel insiders, the ad is being viewed as a sign of a possible “identity crisis” within Southwest. The CrankyFlier bashes the commercial, which is probably unsurprising given the name of the blog. “This ad is just pure … bleh,” the post states. “It says nothing to me. This could be for Southwest or any other legacy airline.”

No song lyrics are audible during the ad, but the CrankyFlier’s Brett Snyder identifies the tune playing in the background and notes that the chorus ironically includes the line “Oh, Lord, I’m still not sure what I stand for.”

One reason that Southwest seems to be saying it no longer stands (just) for low fares is that, in recent studies, the airline has been shown to not always have the cheapest flights. The research firm Topaz International conducted a survey of 100 routes flown by Southwest, and here’s what it discovered:

When comparing airfare only, competing airlines were lower than Southwest Airlines over 60% of the time, and higher than Southwest Airlines 35% of the time. This result is surprising given the perception in the marketplace, and with many travel managers, that Southwest Airlines is in fact the low-cost carrier in all markets they serve.

The study seems to confirm the data dug up by the Wall Street Journal’s Scott McCartney in 2011, when the travel columnist reported that Southwest’s flight prices had risen substantially — up 39% over the preceding five years, compared with 10% for the industry as a whole — and that it tended to charge more on routes where it was the dominant carrier.

It must be noted, however, that the Topaz results above are based on “comparing airfare only,” without incorporating the costs of checked bags. For years, Southwest has loudly celebrated its “bags fly free” policy in ads playing up the value it offered travelers compared with nearly all other airlines — which can charge $25 and up for each piece of checked luggage. When the costs of one checked bag were factored in, Topaz found that Southwest was the cheapest option 60% of the time.

Though the CrankyFlier’s Snyder is obviously not a fan of Southwest’s new commercial because it makes it seem like every other airline out there, he says Southwest is still different from the competition in a few key ways. “The most obvious difference is that Southwest hasn’t gone with the a-la-carte model of pricing and instead continues to bundle things like bag fees and change fees into the price of the ticket,” Snyder said via e-mail. “That’s why you often see that Southwest isn’t the cheapest anymore.” Also, Southwest’s customer-service model, loaded with “employees that are empowered to solve problems,” is generally superior to the ham-fisted bureaucracies in other airlines’ customer-service departments, according to Snyder.

So even as fares have risen, Southwest still sets itself apart with good customer service and the checked-bags value proposition. But for how long? Southwest has already been following the industry’s lead by adding new fees for services like priority boarding, and more nickel-and-diming practices seem inevitable. Snyder worries that Southwest will struggle to maintain top-notch service, especially since it swallowed AirTran — which was also known as a low-fare carrier, but one with a very different customer-service environment.

At SmarterTravel.com, frequent-flyer expert Tim Winship reported that Southwest CFO Tammy Romo stated at a conference that the airline would be tightening restrictions on flights this year. She was also extremely noncommittal about whether Southwest would maintain its long-standing “bags fly free” policy:

I don’t think our brand is Bags Fly Free, that’s not who we are. As I mentioned, our brand is the affordable fares that you get with Southwest and the friendly, warm service that you get from our employees. So I don’t think — an advertising campaign is not your brand. So at least, that’s my belief. And we’ll continue to look at our plan and adjust as we need to meet our financial objectives.

George Hobica, who runs AirfareWatchdog.com, says Southwest may very well be “de-emphasizing ‘bags fly free’ as a prelude to start charging for bags.” No plans have been announced, however. Regardless, based on how big and powerful Southwest has become, and based on the image projected in its new ad campaign, no one should continue to view the airline as an offbeat little upstart company.

“Bottom line, we now really have four major domestic carriers,” says Hobica. “Southwest is one of the big boys now and wants to be recognized as such.”